Method of making hyposulfites by means of amalgam



Nov. 27, 1 s. z. AVEDIKIAN 2, 7 7

METHOD OF MAKING HYPOS ULFITES BY MEANS OF AMALGAM Filed Oct. 25 1950 AMALGAM RESERVO/R 0 Tl 7 F/LOZER V pH 66% FLOW p CELL J /4 V v RESERVo/ 55 DRAIN I \NVENTOR ATTORNEY Patented Nov. 27, 1951 UNITED. STATES... PATENT QF E METHOD OF MAKING HYPOSUL'FIIES BY MEANS OF AMALGAM semen z. Avedikian, Larchmont, Y Application ctober23, 1950, Serial No. 191,583

8 Claims. (01. 23-116)" This invention relates to the manufacture of 'hyposulfites, for example, to the production of sodium hyposulfite, Nazszoi, known commercially as sodium hydrosulfite. More particularly the invention relates to the manufacture by the direct reduction of the bisulfite in aqueous medium by means of the amalagam' of the metallic element thehyposulfite of which it is desired to produce. Specifically, in the production of sodium hyposulfite, sodium bisulfite in' aqueou medium is re- 4. The reduction of sodium bisulfite and/or sulfur dioxide by means-of sodium or ammonium formatey p p 5. The reaction of sulfur dioxide on zinc suspended in water to give zinc hyposulfite and treatment thereof with-sodiun'i'hydroxide or sodium carbonate to give precipitate of zinchydroxide or zinc carbonate in a solution of sodium hyposulfite, separating the precipitate from the solution by filtration or otherwise, and treating the solution further to recover sodium hyposulfite.

Of all the methods cited above, only the fifth has been applied commercially. Despite claims made of high yields, none of the methods cited in the prior art have been found economically practicable except the fifth. It is understood that the second is now used to a limited degree, its extensive application being limited by the utilization that can be made of organic by-products.

The I. G. Farben at Leverkusen, Germany, used the mercury cell to produce sodium amalgam .to make sodium hydrosulfite when the price of zinc was high. At one time 30 to 50 tons of sodium hydrosulfite per month were made from sodium amalgam. The process was discontinued when the price of. zinc dropped. The overall yield was 52-53% on the current. Thi excerpt is fromFIAT Final Report No. 818 dated June 25, 1946 entitled Use of Sodium Amalgam for Reduction of Nitrobenzene and Other Organic Compounds and Production of Sodium Hydrosulfite,

by William C. Gardiner of Technical Industrial Intelligence Branch, U. S, Department of Commerce. It explains the reason for non-application of the method to date despite claims of high yields in the literature of record of th prior art.

It is an object of this invention to provide an improved method for making hyposulfite in accordance with the' principles of the first method described. above. More specifically, it i an object of this invention to make thefirst method com merciallypractical by increasing substantially the yield of. hyposulfite obtained in proportion to the power required; power being a substantial elementofcost.

More specifically, it is an object of this invention to make sodium hyposulfite and other alkali metal hyposulfites such as those of potatssium and lithium, more expenditiously and cheaply than by known methods. 'In addition to the high yield obtained, thisinvention has the further advantage of providing a practical process in which the 'hypo'sulfite is precipitated out during the course of reaction thusmaking possible continuous operation. r V l Other objects, features and advantage of the invention 'will'appear or be pointed out as the specification proceeds? The drawing is'a"diagrammatic' view 'of one apparatus by which the process of this invention can becarried out.

In order to produce sodium hyposulfite, in accordance with-the process of this invention, I use sodium amalgam to reduce the bisulfite ion, (HSO3) in aqueous medium, to hyposulfite ion, (S2O4)=.

It was a most unexpected result, but I found that if I use an amalgam containing a concentration of 0.04% sodium, by weight, namely, substantially that percentage of metallicsodium alloyed with or dissolved in'99.96%"metallic mercury by weight, the sodium in the amalgam functions almost exclusively. in reducing bisulfite to hyposulfite, in accordance with the following equation:'

2Na (from sodium. amalgam 2NaI-ISOa- NazSzO4+2NaOH (1) All references to percentages in the description that follows and the claims are by weight.

At a sodium concentration substantially greater I. than 0.04%, the sodium is spentin what I call the 3 yield of the desired end product. This water reaction is illustrated by the equation sively lower, for example, as low as yields of the order of 25% or less. The concentration of sodium in the amalgam should alwaysdiedower-than' approx maely 0.1%.

I have also discovered that the timeotcontaot between sodium amalgam and the hyposulfite so: lution should be kept at a n'ii'riimiim to *I'EdlllCE or prevent side reactions. substantially identical conditions, except for the presence -01: absence of amalgam, decomposition of hyposulfite originally piES'efitin-a systemis of the order of 20% 40% ormnr ewhan the hyposulfite is in contact'with amalgam-whereas in the absence of amalgam decomposition i's of a much lower magnitude. Furthermore; amalgam favors the conversion of} hypo'sulfite tos'ul fide and thicsulfate. in manner-system described below the time of contact-between amalgam and hyposulfite solution nreducea'tt a minimum aridtlie' surface area'of continuous contact between the amalgam and the solution is's' nall. The resulting. decomposition is ofth ordero'fabout 8% maximum.

I prefer to carry out the reaction between the sodium amalgam andsodiumbisulfite in a tower column ortower M -having abranch conduit H throughwhiehbisulfite solution with which the tower is charged initially, iswithdrawn; This solution passes through acooler 1-3 to a pump I 4 which discharges the solutionthrough a filter or centrifuge l 5 to apH' flow cell l-I- from which the solution passes through a pipe t9 back to the tower HI; Reir igerating medium for the cooler I3 is supplied through pipe 20. The pipe 19 has one branch- 2 l which discharges solution into a branch 22 of the tower, and the-other end of the pipe l9 leads downward to a" discharge outlet 23 near the bottom or the tower-. The solution is thus introduced to the tower both above and below the outlet ll V There is a by-1pass'26 around the filter l5 and there are valves on both sides of the filter l5 and in the by-passline 26 for selectively controlling the flow of liquid through the filter or by-pass. The purpose of this by-pass is to permit opening of the filterand removalof crystals which have accumulated in it without stopping the circulation of liquid through the system;

Amalgam is supplied from a reservoir '28 through piping -30 to andnverted outlet 3| from whichdrops of the amalgam fall into the solution in;the tower The piping 30 includes a shut off valve stand drain valves 34. A gau e 36 exstantial height. I prefer to use in the tower a concentration ofbisuli'ite equivalent to 0.5 to 1.0

The spent amaigam, that is, amalgam which I have found that-under.-

4 has a substantially lower sodium concentration than the amalgam in tially supplied to the tower, drops into a U-tube 40. This spent amalgam 42 eventually fills the U-tube which serves as a trap, and discharges into a spent amalgam reservoir 44 from which the mercury is taken to make new amalgam. V 7

It is necessary, to furnishan.acidic substance to the systemiinx order totregenerate: the bisulfite or to neutralize the" sodium hydroxide formed (see Equation 1 above). Any suitable acid, for example, acetic acid which would not bring about 'a-zsharp drop; inpH-; that is, a sharp increase in hydrogen ion concentration or hydrogen ion activity, can be used. 'Sulfur dioxide gas, especially when supplied by surface absorption, is particularly suitable under the conditions of operation maintained in the tower system. The'sulfur dioxide gas is supplied from a controlled source to a pipe 48. This pipe leads into the space in the-tower I0. abovewthelevel zoffthe liquid. Ipreferto'operate the system.witha the sulfur'dioxide under a slight pressure: im order'to facilitate dissolving of this gas" in the liquid by surface absorption. Thehigher:the-pressure; the greater the amount that will dissolve. This proc'edure makes possible: convenient: control: Off pH at approximately 5 to 6 or at? a; maximum of, 7;.

The. solution in the: tower becomes progressively richer in sodium; hyposulfite: The various reactions taking: place in. the system maybe-represented by the followingrequationsr' 2N'a(from sodium amalgaml Summation of Equations 1 and 3'gives' Equation 4.

The regeneration of bisul'fite takes place in accordance with Equation 5; below.

The sulfur dioxidemay alsobe shown as neutralizing the sodium hydroxide formed (seeEqua- 'tion 6, below).

' Naorr+soa- NaHsoa (6) .I prefer to maintain the systemata temperature of 10 C. or lower... Under these, conditions sodium hyposulfite precipitates out oi solution in practically pure form, .in. well formed crystals that include water of crystallization. I maintain an inert atmosphere throughout the operation except for the sulfur dioxide above the. liquidcon- .tents of the tower. The crystallizationof sodium hyposulfite under these conditions of operation is also a most unexpected result since it occurs at a concentration of only about 6% Whichis the saturation concentration. According to data published in the prior art, solubility of sodium hypo- -sulfite is represented at .1 .C. to'be about .lf6.5%,

the apparatusshown. the crystals are removedin the Qfilter or centrifuge [5 located, beyond, the pump. This filter or :centrifuge couldibe locate aheadof the pump, but ispreferably on thedownstream side of the cooler l 3 because the reduction mam in temperature causes an increase in the precipitation. LI treat the crystals to produce either sodium hydrosulflte of commerce, that is anhydrous sodium hyposulfite, or the formaldehyde complex, that is sodium formaldehyde sulfoxylate.

Instead of or complementary with well known methods of sodium hyposulfite recovery, I have also devised the following method to remove the water of crystallization. I let the crystals fall through a tower filled with alcohol or other suitable and effective dehydrating medium. I maintain the tower at about 52 C., and preferably between 60 and 70 C. The crystals of sodium hyposulfite which I collect from the tower are dried in a vacuum oven. The resulting product is the product of commerce known as sodium hydrosulfite. Sodium formaldehyde sulfoxylate is prepared by reacting the crystals from the amalgam reacting tower system with formaldehyde under suitable conditions.

For purging the tower of air and obtaining inert atmosphere at the beginning of an operation, the tower I0 is equipped with a pipe 52 through which carbon dioxide is introduced into the tower under the control of a shut-off valve 53. This carbon dioxide pipe extends downward through the tower and has a discharge outlet 55 at a low level in the tower. The inert atmosphere supplied to the tower at this low level forces the air out of the tower through a vent 56 which is thereafter closed before the sulfur dioxide supply is introduced into the tower by opening a valve 58.

At the lower end of the tower there is a sampling tube 60 communicating with the tube in which the spent amalgam accumulates. This sam ing tube 60 is commanded by a valve 62 which can be opened whenever it become necessary to take a sample of the amalgam for a test. Another sampling line 64 with a valve 65 can be opened to take samples of the liquid for test purposes.

. From a review of the description of my invention it will be apparent that the process involves three reactions. The first is the reduction reaction which is the productive reaction of the process. This is represented by Equation 1, above, in which the sodium amalgam reacts with the sodium bisulfite in aqueous solution to produce the sodium hyposulfite and the by-products of sodium hydroxide and water. The second is the neutralization of the sodium bisulfite to give sodium sulfite and water. This is represented by Equation 3. The third is the regeneration reaction in which bisulfite is regenerated by furnishing an acidic substance to the system, for example,

sulfur dioxide. This is represented by Equation 5. The second and third reactions may be summarized and the result represented by Equation 6. In the system as operated, it is probable that none of the reactions occur to the exclusion of any of the others and that all take place at some period of the process depending upon the pH at that time. Repetition of the cycle represented by these equations brings about enrichment of the tower solution in respect to sodium hyposulfite finally resulting in its precipitation when its saturation concentration is reached.

With this invention, in which the concentration of the sodium in the amalgam is kept at a very low value, there is very little water reaction, represented by Equation 2 above. The reason for this is not clearly understood. If the concentration is too small, however, the amount of sodium hyposulfite that can be produced within a given time in any particular apparatus is unnecessarily restricted. The concentration of sodium in the amalgam can be as high as 0.04% without causing substantial loss of sodium by the water reaction. The percentage concentration can be increased slightly without producing a substantial waste of sodium, but as the concentration reaches approximately 0.10% of sodium, the waste of sodium becomes large.

The process of the invention has been described in detail for sodium hyposulfite. Potassium hyposulfite, lithium hyposulfite, or any alkali metal hyposulfite can be produced by the'method of this invention by merely substituting the bisulfite of the desired alkali metal for sodium bisulfite and the amalgam of the desired alkali metal for sodium amalgam. For example, to produce potassium hyposulfite, I use potassium bisulfite and potassium amalgam. The apparatus and method are otherwise the same.

The subject matter of this application is related to that of applicants copending application, Serial No. 211656, filed February 19, 1951.

Various changes and modifications can be made and features of the invention can be used alone or in different combinations without departing from the invention as defined in the claims.

I claim as my invention:

1. The method of making an alkali metal hyposulfite which comprises introducing into a body of aqueous solution of said alkali metal bisulphite successive particles of an amalgam of the alkali metal, passing the particles through the body of solution to a collection region, introducing the amalgam into said body of solution with a concentration of less than 0.1% of alkali metal in the amalgam, with-drawing the amalgam at lower alkali metal concentration from the collection region, and withdrawing alkali metal hyposulfite from the body of solution at another region.

2. The methodof making an alkali metal hyposulfite, as described in claim 1, with the amalgam that is introduced into the body of solution having a concentration of the order of 0.04% of sodium and substantially less than 0.1%.

3. The method of making sodium hyposulfite which comprises introducing successive particles of sodium amalgam into a body of aqueous solution of sodium bisulfite, passing the particles through the body of sodium bisulfite solution to a iii) collection region, introducing the sodium amalgam into the body of solution with a concentration of less than 0.1% of sodium in the amalgam, withdrawing the amalgam at lower sodium concentration from the collection region, and withdrawing sodium hyposulfite from the body of solution at another region.

4. The method of making sodium hyposulfite, as described in claim 3 with the body of solution extending downwardly from a top at which the sodium amalgam is introduced into the column so that the sodium amalgam drops by gravity through the body of solution, and in which the collection region is at the bottom of the body of solution, circulating the bisulfite solution through a by-pass from one region of said body of solution to another, and removing sodium hyposulfite from from the bisulfite solution during the passage of the solution through the by-pass.

5. The method of making sodium hyposulfite, as described in claim 3, with the sodium amalgam introduced into the body of solution adjacent to the top of said body sothat the sodium amalgam drops by gravity to the collection region, and in which the sodium amalgam has a concentration of the order of 0.04% of sodium and substan- 

1. THE METHOD OF MAKING AN ALKALINE METAL HYPOSULFITE WHICH COMPRISES INTRODUCING INTO A BODY OF AQUEOUS SOLUTION OF SAID ALKALI METAL BISULPHITE SUCESSIVE PARTICLES OF AN AMALGAM OF THE ALKALI METAL, PASSING THE PARTICLES THROUGH THE BODY OF SOLUTION TO A COLLECTION REGION, INTRODUCING THE AMALGAM INTO SAID BODY OF SOLUTION WITH A CONCENTRATION OF LESS THAN 0.1% OF ALKALI METAL IN THE AMALGAM, WITHDRAWING THEAMALGAM AT LOWER ALKALI METAL CONCENTRATION FROM THE COLLECTION REGION, AND WITHDRAWING ALKALI METAL HYPOSULFITE FROM THE BODY OF SOLUTION AT ANOTHER REGION. 